The use of storage tanks is widespread in such applications as the food, beverage, and pharmaceutical industries, as well as the oil and chemical industries. The need exists to mount microwave instrumentation, such as level sensing apparatus, to tanks or containers in use in such industries to, for example, provide accurate level measurement for inventory control and custody transfer.
Large storage tanks may be on the order of 100 feet (30 meters) deep and 100 to 200 feet (30 to 60 meters) across. Process tanks may be on the order of 10 to 17 feet (3 to 5 meters) deep and 10 to 17 feet (3 to 5 meters) across. Historically, liquid levels have been measured by lowering a device into the tank from a roof-mounted platform. Devices used for this purpose have included long sticks and both manual and automated versions of weighted strings or wires which can be lowered into the tank until the liquid (or solid) content is touched. The depth of the material in the tank, and thus the volume of material in the tank, can then be readily determined from the length of the stick, string, or wire. The early use of sticks has led to the term "sticking the tank" for describing the level measurement procedure. While such mechanical methods have continuously been improved and can achieve a very high accuracy in some applications, all such methods require a physical intrusion of the tank environment. There is thus a potential for contamination of the tank contents and for the corrosion, and the ultimate destruction of the measuring device itself.
Over the past approximately fifteen years, various level measuring devices using radar techniques have been developed. With the use of radar techniques the material to be measured is not touched; however, the antenna which radiates and receives microwave energy in order to make the measurement, is mounted inside the tank. In many tank environments, a corrosive gaseous atmosphere exists in the space above the liquid and the antenna material erodes. The antenna material thus contaminates the tank contents. Other applications may require a hygienic container environment where isolation from sensors is also desirable.
What is needed is a non-intrusive mounting system and method for microwave instrumentation such as level sensing apparatus which can be outside the tank interior atmosphere and have a low vertical profile. Such a system would desirably allow for easy removal of electronic instrumentation in applications such as level sensing and allow for the use of a small antenna, including a planar antenna, in such a system. The apparatus would have a relatively short height compared to existing radar level measurement systems and would handle tank pressures at least to approximately 150 pounds per square inch (psi) (approximately 10.sup.6 pascal). Moreover, such a method and apparatus would desirably accommodate prevalent 2 inch (5.08 cm) and 8 inch (20.32 cm) standard flange openings and be flexible and readily configurable to other desired pipes.